Flotation separators are known in the art. They are useful for the mechanical separation of suspended materials, emulsifiers and colloids which can float and which are found in the water being treated. The materials are conveyed to the surface of a liquid as a result of interaction with a gas. The operation is designated as flotation.
The known apparatuses either use expansion flotation or introduce the gas into the liquid by means of special discharge nozzles or by means of electrolysis.
In the apparatus that uses expansion flotation, a portion of the liquid prior to flowing into the collecting tank is enriched with air under high pressure and mixed with the main liquid stream. When the liquid is introduced into the flotation tank, small bubbles are formed as a result of the sudden reduction in pressure, the small air bubbles interact with the flotable materials so that they are conveyed upwards to the surface. The liquid flowing from the discharge end of the tank forms a main throughput current which conveys the floating mass on the surface of a liquid past the downflow-upflow wall, to the skimmer which skims off the floating mass into a skim channel where it is collected and discharged.
However, this apparatus has the disadvantage that the liquid passes straight through the apparatus and only a one-time contact with the gas occurs. No circulation of the liquid occurs nor is it intended. Therefore, the downflow-upflow wall of the appartus is as a rule shut off at the bottom. The only current is the main throughput current that conveys the floating mass to the skimmer. As a consequence, the liquid is not thoroughly treated, and leaves the tank still charged with impurities. The construction and operation of the apparatus are very costly.
In an apparatus in which the gas contact is effected by means of discharge nozzles, no circulation of liquid and repeated gas contact takes place. The air is introduced into the liquid in the form of small bubbles through small apertures in the walls of the nozzles generally fabricated from sintered material. The formation of the very fine bubbles at first favors the flotation. As time passes, the fine discharge apertures become obstructed and the liquid is not intimately contacted with any gas. In this apparatus, there is the danger that a large portion of the materials are not precipitated.
The present invention is directed to an apparatus of the type mentioned above which can achieve a more thorough treatment of a liquid. The present invention provides a current of liquid that is repeatedly contacted with the gas and at the same time enables the flotable materials in the liquid to be floated and the heavy materials to settle. The fabrication and operation of the apparatus are economical and in addition, the apparatus can be regulated with regard to the rate of flow, height of the liquid level, and portion of portion of water in the skimmed floating mass. Furthermore, the apparatus is useful for the flotation of materials capable of floating and for precipitation of materials that form sediments. In addition, the apparatus can be used for neutralizing solutions and flocculating colloidally dispersed materials and emulsifiers.